A significant concern of both providers and users of satellite communication systems is how to maximize the use of system resources. In particular, transponder bandwidth and effective isotropic radiated power (EIRP) are both important, since some portion of each is employed by every signal sent through the transponder. Because satellite resources are expensive, for the case where satellite power is the scare resource, minimizing the amount of power required for each signal allows more signals to be sent through the transponder, and thereby reduces leasing fees. An alternative application is to reduce the aperture size of the receiver antenna for the same transponder power. Certain relatively low-cost prior art systems that use small aperture antennas tend to be power-limited as they have lower G/T values, and therefore require more power from the satellite.
One particularly advantageous approach for providing enhanced power and bandwidth utilization in such communications systems is disclosed in U.S. Pat. No. 6,606,357 to Cobb et al., which is assigned to the present Assignee and is hereby incorporated herein in its entirety by reference. This patent discloses a technique for injecting a prescribed amount of carrier energy into a waveform, such as a QAM or M-ary phase shift keying (MPSK) waveform (e.g., BPSK, QPSK, 8PSK, etc.). This baseband pilot injected carrier (BPIC) component allows for detection and recovery, as opposed to non-linear regeneration, of the carrier at the receiver.
The BPIC modulation approach is also well suited to take advantage of the enhanced performance of modern forward error correction (FEC) coding schemes, such as turbo codes, for example, to significantly reduce the signal power required for achieving a relatively low bit error rate. Namely, using a prescribed BPIC waveform in combination with advanced coding techniques allows the number of small-terminal users on a satellite transponder to be potentially doubled, thus effectively halving user leasing costs. Conversely, the BPIC waveform also may allow the use of a smaller antenna to provide more flexibility of placement and/or mobility.
Despite the significant advantages of the BPIC modulation approach, additional techniques may be desirable in certain applications to further reduce the overhead associated therewith yet while still enjoying significant power savings.